There are many instances in the prior art in which a web of material is fed continuously through processing apparatus which coats or otherwise treats the web. Also known in the prior art are devices for feeding the web continuously to the process station from a plurality of successive rolls, the ends of which are automatically spliced together without interruption of the web feed.
Many of the automatic web splicers of the prior art form a lap splice in which a portion of the web from the expiring roll overlies a portion of the web from the new roll with the under surface of the overlapped portion of one of the webs adhered to the upper surface of the other web. While such a splice is satisfactory in most instances, it is not suitable in certain cases in which a double thickness of web is not readily tolerated. For example, there are processing systems in which the web being treated must pass through the nip between a pair of closely spaced rolls or through a similar narrow gap. In such a case, particularly where the web is traveling at a relatively high speed, the double thickness of web at the lap splice may damage the apparatus by denting one of the rolls or destroying the roll support bearings. Further, owing to the shock applied to the web in the region of the splice, the web may break even if the apparatus is not damaged. The resultant stoppage of the continuous process obviously is undesirable.
A number of attempts have been made in the prior art automatically to form a butt splice in which the trailing edge of the expiring web butts the leading edge of the new web so that there is no overlap. Such attempts, however, have for various reasons not been as successful as is desired. One of the most difficult problems has been the disposal of the leading edge portion which is cut from the new web in the course of forming the butt splice.
One example of an attempt in the prior art to form a butt splice is shown in DeRoeck et al U.S. Pat. No. 4,097,323. In the arrangement shown in this patent, the web being unwound passes around the portion of the surface of a vacuum drum from about the six o'clock position to about the twelve o'clock position thereof. A new roll is contained by a flexible strap which is held around the roll by a releasable buckle. When the new web is to be spliced to the expiring web, a buckle release roll is brought into operative position to release the buckle within one revolution of the new roll. Once the buckle has been released, the strap falls away and the leading edge of the new roll is fed by a pair of rolls into the space between the expiring web and the vacuum roll at the six o'clock position. Thus, the new web is carried around the vacuum roll together with the expiring web. After the leading edge of the new web has thus been introduced between the vacuum drum and the expiring web and at approximately the five-thirty location on the vacuum drum, both webs are cut. The vacuum drum is provided with an indentation for permitting this operation to be achieved. After the cut is made, the tail of the expiring web falls away or is carried away by the knife roller. At about the three o'clock position on the vacuum drum, a taping roll applies a length of tape to the cut ends of the web to form the butt splice. At the twelve o'clock position the expiring web to which the new web has been spliced is carried away by a takeoff roller and the leading portion of the new web which is severed by the knife roll is discharged.
Not only does the DeRoeck system involve the complication of holding the new web with a flexible strap and releasable buckle and the buckle release mechanism, but also no provision is made for ensuring that the severed leading portion of the new web is not separated from both the expiring web and the surface of the vacuum drum in such a way that it will not interfere with the unwinding operation or a subsequent process.